This invention relates to valve gated injection molding and more particularly to improved valve pin actuating mechanism wherein a resilient O-ring and a compressible retaining ring are used to removably connect the valve pin to the piston.
In a hydraulically actuated valve gated injection molding system, it is necessary that the valve pin be securely connected to the piston, but it is also desirable that it be easily removable. It is also necessary that the connection not cause or permit the leakage of pressurized hydraulic fluid from the cylinder.
In the past, a variety of arrangements have been used to connect the valve pin to the piston. One of these is shown in U.S. Pat. No. 4,468,191 to Gellert entitled "Hydraulically Actuated Injection Molding with Alternate Hydraulic Connections" which issued Aug. 28, 1984. This patent shows the valve pin extending through the piston and having an enlarged head which is seated in the piston and held in place by a threaded cap or plug. While this arrangement is satisfactory for many applications, it has the disadvantages that the threads do not always provide a secure seal against leakage between them and also the threaded cap must be relatively thick which is a problem in application where minimum mold height is desirable.
German patent number DE No. 3,336,258C2 dated Apr. 17, 1986 to Hasko Normalien Hasenclever & Co shows a valve pin which is held in place by a resilient retaining ring. However, there is not adequate provision against leakage of pressurize hydraulic fluid past the valve pin.